fpt Reference: STRUCTURE ALIGNMENT GRANULARITY

fpt and WinFPT Reference Manual - Command-line Commands

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STRUCTURE ALIGNMENT GRANULARITY

Syntax:

STRUCTURE ALIGNMENT GRANULARITY [:] <integer> [BYTE[S]]

Function:

Most systems access memory more efficiently if objects occupy aligned addresses, ie. addresses which are multiples of 4 or 8 bytes. Some compilers will leave empty spaces within derived types and structures in order to align the addresses of the type components and structure fields. The command STRUCTURE ALIGNMENT GRANULARITY specifies the spacing of aligned addresses. The command ALIGNMENT GRANULARITY specifies the spacing of aligned addresses of local variables and of variables in COMMON blocks.

By default fpt assumes that objects in derived types and structures are not forced to aligned addresses. fpt may be instructed to leave spaces in derived types, structures and COMMON blocks by the commands ALIGN OBJECTS IN STRUCTURES and ALIGN OBJECTS IN COMMON BLOCKS.

The alignment granularity rules used by most compilers, and by fpt, are that:

the alignment granularity of a logical, integer or real type component or field is the data size of the type component or field, or the structure alignment granularity, whichever is the smaller;
the alignment granularity of a complex field is the data size of the real data specification with the same kind, or the structure alignment granularity, whichever is the smaller;
the alignment granularity of fields which are character variables and character arrays is one byte, but access is more efficient if variables and array elements start on aligned addresses;
the alignment granularity of a record or of a derived type is the granularity of the largest object in the structure or type, or the structure granularity, whichever is the smaller.

Where to Use this Command

Operating system command line	Yes
Configuration file, config.fsp	Yes
Specification (fsp) files, *.fsp	Yes
Interactively, to FPT> prompt	No
Interactive command files	No
Embedded in the Fortran code	No

Note that the alignment granularity used by the command ALIGN OBJECTS IN STRUCTURES cannot be specified interactively because addresses within derived types and structures are computed before fpt enters interactive mode.

Default

STRUCTURE ALIGNMENT GRANULARITY : 4 BYTES